Production of alkenyl alkanoate catalysts

ABSTRACT

This invention provides a process for producing improved catalysts for the production of alkenyl alkanoates by the reaction of an alkene, an alkanoic acid and an oxygen-containing gas. The catalysts contain palladium, gold and a potassium promoter and are characterized by a reduced sodium content which results in increased catalyst activity. The reduced sodium content is obtained by using essentially sodium-free starting materials in the process for producing the catalysts.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 696,215; filed May 6, 1991.

FIELD OF THE INVENTION

This invention relates to a process for producing catalysts (hereinafterreferred to as "alkenyl alkanoate catalysts") for the production ofalkenyl alkanoates from alkenes, alkanoic acids and an oxygen-containinggas.

DESCRIPTION OF THE RELATED ART

Processes for producing alkenyl alkanoate catalysts are known. By way ofillustration, British Patent 1,215,210 (National Distillers) discloses aprocess for the production of olefinically unsaturated carboxylic esters(e.g., vinyl acetate) comprising reacting an olefinically unsaturatedcompound, a carboxylic acid and oxygen in the presence of a catalystcontaining palladium metal and platinum metal and activated with atleast one alkali metal or alkaline earth metal hydroxide or organic acidsalt or inorganic acid salt.

The alkenyl alkanoate catalysts of National Distillers are produced by:(1) dissolving salts of the metals in conventional solvents, (2)spraying the solutions on an inert carrier or soaking the inert carrierin the solutions, (3) removing the solvent, (4) converting the salts sodeposited on the carrier to the free metals: (a) by thermaldecomposition, (b) by reduction with hydrogen or (c) by reduction insuspension using aqueous alkaline formaldehyde, aqueous hydrazine oraqueous or alcoholic sodium borohydride, (5) washing the catalyst withwater to remove chlorides (see the National Distillers Examples) and (6)activating the catalyst. In the National Distillers catalyst preparationprocedure, there is no precipitation of the metal salts on the carrierprior to their conversion to the free metals.

The National Distillers' alkenyl alkanoate catalysts are activated witha minor amount of at least one alkali metal or alkaline earth metalhydroxide or organic acid salt or inorganic acid salt. The alkali metalor alkaline earth metal salts of weak acids, both organic and inorganicacids are stated to be especially useful as activators. Sodium, lithium,potassium, rubidium and cesium salts and mixtures thereof are stated tobe most effective as activator and the use of sodium and potassiumsalts, e.g., sodium and potassium acetates is especially preferred. Thesalts may have such anions as citrate, acetate, borate, phosphate,tartrate, benzoate or aluminate. National Distillers discloses thatalkali metal and alkaline earth metal hydroxides are also effectiveactivators and that the use of halide anions should preferably beavoided, since the presence of halides is stated to deleteriously affectthe synthesis reaction.

In both of the National Distillers' Examples the salts were reduced withhydrogen and washed with water to remove chlorides. Then the catalystswere treated with aqueous solutions containing both sodium acetate andpotassium acetate and dried in a rotary evaporator and then undervacuum. Based on the amount of sodium acetate used, the resultingcatalysts contained about 0.23 weight percent sodium. The most activecatalyst of the National Distillers' Examples (i.e., the catalyst ofExample 2H) is disclosed as having an activity of 8.3 grams of vinylacetate per gram of palladium per hour (equivalent to about 165 grams ofvinyl acetate per liter of catalyst per hour, assuming a catalystdensity of one gram per milliliter).

As another illustration, Journal of Catalysis, volume 17, pages 366 to374, 1970 (Nakamura et al.) discloses vinyl acetate catalysts producedby impregnating a carrier (calcined alumina) with an aqueous solution ofpalladium chloride, evaporating to dryness, reducing with an alkalinehydrazine hydrate solution, washing with distilled water to removechloride ions, impregnating with a metal salt solution (e.g., apotassium or sodium acetate solution) and drying. Nakamura et al.reports that impregnating with potassium acetate results in a catalystactivity of 25 grams of vinyl acetate per hour per liter of catalystwhile impregnating with sodium acetate results in a catalyst activity of19 grams of vinyl acetate per hour per liter of catalyst.

As a further illustration, U.S. Pat. No. 3,743,607 (Sennewald et al.)discloses a process for making vinyl acetate from ethylene, acetic acid,and molecular oxygen or air in the gas phase. A mixture of thesereactants is passed in contact with a supported catalyst containingmetallic palladium, an alkali metal formate or acetate, and metallicgold.

The vinyl acetate catalysts of Sennewald et al. are produced byimpregnating a catalyst carrier with an aqueous solution of a palladiumsalt and a gold salt and the resulting mixture is evaporated to dryness.The mass so obtained is introduced into an aqueous solution containingan appropriate reducing agent (e.g., hydrazine) that is capable ofreducing both the palladium and gold salts to the metallic state. In theSennewald et al. catalyst preparation procedure, there is noprecipitation of the salts on the carrier prior to the reduction. Oncethe reduction is complete, the catalyst mass is removed from the liquidby filtration and washed with water. When the reduction is achieved bymeans of a reducing agent free of alkali (e.g., hydrazine), the catalystis conveniently impregnated with an about 10% solution of sodiumacetate. The formates or acetates of lithium or potassium can also beused. The catalyst is then dried and is ready for use. Sennewald et al.discloses that, in the absence of such treatment, despite the gold itcontains, the catalyst is found to have a substantially lower activity(e.g. an activity of only 15 grams vinyl acetate per liter of catalystper hour) instead of the activity of 50 to 120 grams vinyl acetate yieldper liter of catalyst per hour disclosed in Sennewald et al. for theSennewald et al. catalysts. Catalysts which have been reduced by meansof a composition comprising sodium formate and formic acid are disclosedto be active, even if no sodium acetate has been added thereto.

Sennewald et al. states that it has unexpectedly been found that thevinyl acetate space/time yields and, more particularly, the lifetime ofthe supported catalyst until regeneration thereof, can be substantiallyincreased when the catalyst is impregnated with a solution prepared froma mixture of various acetates of sodium, potassium, rhodium or cesiuminstead of impregnation with a solution of a single alkali metalacetate.

The highest activity reported in the Sennewald et al. Examples is inExample 11 where a catalyst was impregnated with sodium and potassiumacetate as described in Example 9 of Sennewald et al. To effect theimpregnation, the catalyst was introduced into a solution of theacetates, the supernatant solution was decanted and the catalyst wasdried. The catalyst so obtained in Example 11 of Sennewald et al. isreported to contain about 0.8% sodium and to have an activity of 146grams of vinyl acetate per liter of catalyst per hour. The otherSennewald et al. Examples (including Examples 4, 5 and 12(e) where thecatalysts were apparently substantially free of sodium) reported evenlower catalyst activities than Example 11. The catalysts of Sennewald etal. Examples 4 and 9 were reported to have the same palladium and goldcontents and approximately the same activities. The catalyst of Example4 is reported to contain 2.5% potassium (as potassium acetate) while thecatalyst of Example 9 is reported to contain about 1.8% sodium (assodium acetate).

U.S. Pat. No. 3,822,308 (Kronig et al.) discloses that particularlyactive supported catalysts containing palladium and gold for theproduction of vinyl esters from ethylene, lower carboxylic acids with 2to 4 carbon atoms and oxygen in the gas phase at elevated temperatureand at normal or elevated pressure are obtained by the followingprocedure: The catalyst support is treated, simultaneously orsuccessively, with or without intermediate drying, with a solution("Solution A") containing dissolved salts of palladium and gold and,optionally, salts of other metals, and another solution ("Solution B")containing compounds (hereinafter referred to as "precipitating agents")which are able to react on the catalyst support with the noble metalsalts of the Solution A to form water-insoluble noble metal compoundswhich are practically free from halogen, sulphur and nitrogen. SolutionsA and B (separately or in combination) are used to impregnate thecatalyst support in quantities which correspond to from 10 to 110% ofthe absorptive capacity of the catalyst support for these solutions. Thecatalyst support impregnated with Solutions A and B is subjected to atime/temperature treatment such that at least 95% of the impregnatedpalladium and at least 95% of the impregnated gold are transformed intowater-insoluble noble metal compounds. The water-insoluble noble metalcompounds are largely transformed by treatment with reducing agents intothe noble metals and the water-soluble compounds which are contained inthe catalyst are removed by washing, before or after the reduction.

In a preferred embodiment of the Kronig et al. process, alkali metalcarboxylates (especially alkali metal acetates) are applied on thecatalyst before or after the treatment with reducing agents in suchquantities that the catalyst, after being dried, contains from 1 to 30%by weight of alkali metal carboxylate. Examples of the alkali metalcarboxylates disclosed in Kronig et al. include sodium formate,potassium acetate, sodium acetate, lithium acetate, potassium propionateand potassium butyrate.

The Kronig et al. Examples employing precipitating agents reportcatalyst activities markedly higher than the activities reported byNational Distillers and Sennewald et al. where no precipitating agentsare used. Thus, Kronig et al. Example 1 employs sodium hydroxide as aprecipitating agent and potassium acetate as a promoter and reports aactivity of 452 grams of vinyl acetate per hour per liter of catalyst.Kronig et al. Example 3 employs potassium carbonate as a precipitatingagent and an "alkali metal acetate" as a promoter and reports that theresults obtained with the catalyst were comparable to those of Kronig etal. Example 1.

U.S. Pat. No. 4,048,096 (Bissot) discloses a catalyst having a specificactivity of at least about 83 grams of vinyl acetate per gram ofprecious metal per hour measured at 150° C. The Bissot vinyl acetatecatalyst consists essentially of: (1) a catalyst support having aparticle diameter of from about 3 to about 7 mm and a pore volume offrom about 0.2 to about 1.5 ml./g., a 10% by weight water suspension ofthe catalyst support having a pH of from about 3.0 to about 9.0; (2) apalladium-gold alloy distributed in a surface layer of the catalystsupport, the surface layer extending less than about 0.5 mm from thesurface of the support, the palladium in the alloy being present in anamount of from about 1.5 to about 5.0 grams per liter of catalyst, andthe gold being present in an amount of from about 0.5 to about 2.25grams per liter of catalyst, and (3) from about 5 to about 60 grams perliter of catalyst of alkali metal acetate. Bissot discloses that thepalladium is the active catalyst metal and the gold is a catalystpromoter.

Bissot also discloses a process for preparing the Bissot catalyst. LikeKronig et al., the Bissot process involves precipitation of the metalsalts on the catalyst support. The Bissot process comprises: (1)impregnating the catalyst support with aqueous solution of water-solublepalladium and gold compounds, (2) precipitating water-insolublepalladium and gold compounds on the catalyst support by contacting theimpregnated catalyst support with a solution of compounds (preferablysodium metasilicate) capable of reacting with the water-solublepalladium and gold compounds to form water-insoluble palladium and goldcompounds, (3) converting the water-insoluble palladium and goldcompounds into palladium and gold metal on the support by treatment witha reducing agent, (4) washing the catalyst with water, (5) drying thecatalyst (see Example 1 of Bissot), (6) impregnating the catalyst withalkali metal acetate promoter (e.g., a potassium promoter), and (7)drying the catalyst.

The improvement disclosed in Bissot involves distributing the palladiumand gold as an alloy in a surface layer of the catalyst support, thesurface layer extending less than about 0.5 millimeter from the surfaceof the support. The impregnating step is carried out with an aqueoussolution of palladium and gold compounds and the total volume of thesolution is from about 95 to about 100% of the absorptive capacity ofthe catalyst support. The precipitating step in Bissot is carried out bysoaking the wet catalyst support with a solution of an alkali metalsilicate, the amount of alkali silicate being such that, after thealkali metal silicate solution has been in contact with the catalystsupport for about 12 to 24 hours, the pH of said solution is from about6.5 to about 9.5.

Bissot does not report the sodium content of the catalysts of the BissotExamples. Bissot Example 1 reports that the catalyst of that Example hadan activity of 560 grams of vinyl acetate per liter of catalyst perhour. In Example III below, two catalysts produced following thedisclosure of Example 1 of Bissot were found to have sodium contents of0.32 and 0.38 weight percent and activities of 551 and 535 grams ofvinyl acetate per liter of catalyst per hour.

Despite the foregoing prior art processes, it is desirable to furtherimprove the activity of alkenyl alkanoate catalysts.

SUMMARY OF THE INVENTION

This invention is based, in part, on the discovery that the activity ofalkenyl alkanoate catalysts is increased if their sodium content isdecreased by employing essentially sodium free starting materials inproducing the catalyst.

More specifically, this invention provides a process for producing acatalyst that is useful in catalyzing the reaction of an alkene, analkanoic acid and an oxygen-containing gas to produce an alkenylalkanoate and that comprises support particles which are capable ofexchanging cations and which are impregnated with palladium, gold andpotassium acetate: said process comprising the steps of:

(a) impregnating the support particles with aqueous solutions ofwater-soluble palladium and gold compounds;

(b) precipitating water-insoluble palladium and gold compounds onto thesupport Particles from such solutions using a precipitating agent;

(c) converting the precipitated water-insoluble palladium and goldcompounds to palladium and gold on the support particles using areducing agent;

(d) washing the support particles with water;

(e) drying the support particles;

(f) further impregnating the support particles with a potassiumpromoter; and

(g) drying the impregnated particles to produce the catalyst; and saidprocess being conducted by employing essentially sodium-free startingmaterials in steps (b) and (c) so as to reduce the amount of sodium inthe catalyst and thereby to increase the activity of the catalyst.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the predicted effect of sodium on the performance of vinylacetate catalysts produced in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the practice of the process of the present invention,sodium-containing, water-soluble palladium and/or gold compounds canusually be employed since they are usually not used in amounts thatresult in catalysts having substantial amounts of sodium. The principalsources of sodium in alkenyl alkanoate catalysts are sodium-containingprecipitating agents (e.g., sodium metasilicate) and/orsodium-containing promoters or activators (e.g., sodium acetate). To alesser extent, some supports and some reducing agents (e.g., sodiumborohydride) can introduce substantial amounts of sodium into thecatalyst. Accordingly, in the practice of this invention, essentiallysodium-free precipitating agents (e.g., potassium hydroxide), promoters(e.g., potassium acetate), reducing agents (e.g., hydrazine) andcarriers are employed. When using potassium hydroxide as theprecipitating agent, a suitable potassium salt (e.g., potassium acetate)can also be used in the precipitating step to aid in displacement bypotassium of any sodium bound on the carrier. Preferably the potassiumhydroxide and the potassium salt are employed in an aqueous solution.The salt is used in an amount that provides from 1 to 10 weight percentpotassium based on the total weight of the solution. Care should beexercised to ensure that the resulting catalyst does not contain so muchpotassium that catalyst activity is less than desired.

The support particles used in the process of this invention are solidparticulate materials that are capable of exchanging cations (e.g., dueto the presence of SiOH or AlOH groups), that are capable of beingimpregnated with palladium, gold and a potassium promoter and that areinert under the conditions used to produce alkenyl alkanoates.Illustrative of such support particles are particulate silica, alumina,and silica-aluminas. Silica is the preferred support. The supportpreferably has a surface area from 100 to 800 square meters per gram.

The aqueous solutions of water-soluble palladium and gold compounds usedin the process of this invention include aqueous solutions of anysuitable palladium or gold compound such as palladium (II) chloride,sodium tetrachloropalladium (II) (Na₂ PdCl₄), palladium (II) nitrate,palladium (II) sulfate, gold (III) chloride or auric (III) acid(HAuCl₄). The volume of the solution preferably corresponds to from 95to 100% (more preferably from 98 to 99%) of the pore volume of thesupport.

The precipitating agents used in the process of the present inventioninclude lithium and potassium silicates and hydroxides. Theprecipitating agents are preferably employed in the form of aqueoussolutions containing a 1.6 to 1.8 molar excess of the precipitatingagents. The volume of such solution used is preferably just sufficientto cover the support particles. To avoid possible degradation of thesupport, the weight ratio of the precipitating agent to the supportshould not be too high. By way of illustration, a weight ratio ofpotassium hydroxide to support of about 0.08:1 resulted in no noticeabledegradation of the support.

The reducing agents used in the process of this invention includeethylene, hydrazine, formaldehyde and hydrogen. The reducing agents arepreferably employed in the form of aqueous solutions containing a 50:1(or more preferably a 10:1) molar excess of the reducing agents. Ifhydrogen is used, it is usually necessary to heat the catalyst to 100 to300° C. to complete the reduction.

The potassium promoters used in the process of this invention includepotassium alkanoates and any potassium compound that is converted to apotassium alkanoate during the alkenyl alkanoate-forming reaction (i.e.,the reaction of ethylene, an alkanoic acid and an oxygen-containing gasin the presence of the catalyst to produce an alkenyl alkanoate).Suitable potassium compounds include potassium acetate, bicarbonate,nitrate and (when a stable support is used) hydroxide. The promoters arepreferably applied in the form of aqueous solutions.

The washing step in the process of this invention can be conductedbatchwise or continuously. Continuous washing is more efficient but maynot be most suitable for large scale (e.g., plant scale) catalystProduction. In continuous washing, the wash water is slowly andcontinuously passed through the catalyst over a period of time (e.g.,from 8 to 24 hours). In batch washing, the catalyst is contacted withthe wash water, the mixture is allowed to stand (e.g., for from 0.5 to2.0 hours) and the water and catalyst are separated. In batch washing,several such washes (e.g., from 2 to 10, or preferably from 4 to 6washes) are often required to reduce the impurity (e.g., halide) contentof the catalyst to the desired level. Temperatures from 20° C. to 80°and volume ratios of wash water to catalyst of from 2:1 to 100:1 can beused in either batch or continuous washing. The washing step removescertain impurities, particularly chlorides, from the catalyst.

The drying of the catalyst in accordance with step (e) and step (g) ofthe process of this invention for producing alkenyl alkanoate catalystscan be conducted in any convenient manner. By way of illustration,drying can be conducted at 40° C. to 120° C. in a forced air oven for 15to 30 hours.

The catalyst produced by the process of this invention are useful incatalyzing the reaction of an alkene, an alkanoic acid and anoxygen-containing gas to produce an alkenyl alkanoate and comprisesupport particles which are capable of exchanging cations and which areimpregnated with precipitated and reduced palladium and gold and apotassium promoter, any sodium in the catalyst being preferably presentin an amount no more than 0.3 weight percent based on the total weightof the catalyst.

The catalysts produced by the process of this invention preferably havea palladium content of greater than 0.25 weight percent based on thetotal weight of the catalyst, more preferably greater than 0.5 weightpercent based on the total weight of the catalyst and most preferablyfrom 0.5 to 1.7 weight percent based on the total weight of thecatalyst. It is preferred that the gold to palladium weight ratio of thecatalyst is from 0.2 to 1.5 and, most preferably, from 0.4 to 1.2

The catalysts produced by the process of this invention desirablycontain no more than 0.3 weight percent sodium based on the weight ofthe catalyst. Preferably the catalysts contain no more than 0.2 weightpercent sodium and, most preferably, the catalysts contain no more thanabout 0.1 weight percent sodium based on the weight of the catalyst. Theamount of sodium in the catalysts of this invention will dependprimarily on the particular starting materials used and, to a lesserextent, on the number of washes, the volume of wash water and the totalwashing time.

It is preferred that the catalysts produced by the process of thisinvention are shell impregnated catalysts wherein a catalyst support hasa particle diameter from about 3 to about 7 millimeters and a porevolume of 0.2 to 1.5 milliliters per gram. The palladium and gold arepreferably distributed in the outermost 1.0 millimeter thick layer ofthe catalyst support particles. The catalysts preferably contain fromabout 1.4 to about 3.8 weight percent (and more preferably from 2 to 3.6weight percent) of the potassium derived from the potassium promoter.

The catalysts produced by the process of this invention arecharacterized by their increased catalytic activity. Typically theactivity of the catalysts is 5% to 25% greater (in terms of quantity ofalkenyl alkanoate produced per unit of catalyst per unit time) thanotherwise identical catalysts containing from over 0.3 to about 1.0weight percent sodium. Although catalyst selectivity (i.e., the tendencyto produce alkenyl alkanoates rather than by-products such as carbondioxide) declines somewhat with decreasing sodium content, thatdisadvantage is more than offset by increased catalyst activity,particularly in the range of sodium contents found in commercial alkenylalkanoate catalysts (e.g., up to about 1.0 weight percent sodium).

The process for producing alkenyl alkanoates using the above-describedcatalysts ("alkenyl alkanoate process") comprises reacting an alkene, analkanoic acid, and an oxygen-containing gas in the presence of acatalytic amount of catalyst of this invention as described above. Thealkenyl alkanoate process is preferably conducted at a temperature from100° C. to 250° C. (and most preferably at a temperature from 140° C. to200° C.) and at a pressure from 15 psi to 300 psi (most preferably at apressure from 90 pounds per square inch to 150 pounds per square inch.)The alkenyl alkanoate process is preferably conducted continuously inthe vapor phase.

Preferred alkanoic acid starting materials used in the alkenyl alkanoateprocess contain from two to four carbon atoms (e.g., acetic, propionicand butyric acid). Preferred alkene starting materials contain from twoto four carbon atoms (e.g. ethylene, propylene and n-butene). Preferredproducts of the alkenyl alkanoate process are vinyl acetate, vinylpropionate, vinyl butyrate, and allyl acetate.

The alkenyl alkanoates produced by the alkenyl alkanoate process areknown compounds having known utilities (e.g., vinyl acetate is useful inproducing polyvinyl acetate).

Other process for producing alkenyl alkanoate catalysts having reducedsodium content (and so increased catalyst activity) are described andclaimed in the U.S. patent application Ser. No. 07/793,129, allowed,entitled Catalysts for Alkanoate Production and U.S. patent applicationSer. No. 07/793,127, allowed, entitled Alkenyl Alkanoate CatalystProcess, both filed concurrently herewith in the name of the instantapplicant.

EXAMPLES

In the following Example, the following abbreviations are used:

    ______________________________________                                        Abbreviation   Meaning                                                        ______________________________________                                        Support I      Silica beads having an                                                        average diameter of 5 to 6                                                    millimeters and containing                                                    about 0.1 weight percent                                                      sodium. The beads have a                                                      surface area from 150 to 200                                                  square meters per gram and a                                                  pore volume from 0.6 to 0.7                                                   milliliters per gram.                                                         Support I contains SiOH                                                       groups that are capable of                                                    exchanging cations. Support                                                   I is sold by Sud Chemie AG                                                    as "KA-160"                                                    STY*           Space Time Yield (a measure                                                   of catalyst activity)                                                         expressed as grams of vinyl                                                   acetate per liter of                                                          catalyst per hour.                                             % Selectivity* Selectivity was calculated                                                    as follows: Selectivity =                                                     100 X (moles vinyl                                                            acetate)/(moles vinyl                                                         acetate + 1/2 X moles CO.sub.2)                                AA Analysis    Atomic Adsorption                                                             Spectroscopy                                                   ICP            Inductively Coupled Plasma                                                    Optical Emission Spectrometry                                  g VA/l cat/hr  Grams of vinyl acetate                                                        produced per liter of                                                         catalyst per hour                                              ______________________________________                                         *All the values for activities and selectivities reported in the Examples     appearing below are based on the activities and selectivities measured        twentysix hours after full oxygen feed was reached in the Catalyst Test       Method described below.                                                       VA vinyl acetate                                                              KOAc potassium acetate                                                        EcOAc ethyl acetate                                                           NaOAc sodium acetate                                                          % percent by weight                                                           g grams                                                                       ml milliliter                                                                 mm millimeter                                                                 hrs hours                                                                     min minute                                                               

In the following Examples, the following procedures were used:

Catalyst Preparation Procedure

Support I (15 g) was added to a solution of Na₂ PdCl₄ (35.86% Pd, 0.258g) and HAuCl₄ (48.95% Au, 0.094 g) dissolved in 9.0 ml of deionizedwater. The mixture so formed was gently agitated until all of themoisture was absorbed into the support and then was allowed to stand ina sealed flask for about one hour at room temperature so as toimpregnate the support with the palladium and gold salts. The dampcatalyst was covered with a solution of potassium hydroxide (0.371 g in28 ml water) as a precipitating agent. Potassium acetate is used inconjunction with potassium hydroxide in the precipitation step in apreferred embodiment of this invention. After mixing for a few seconds,the mixture was allowed to stand covered and undisturbed for 23 hours atroom temperature to deposit water-insoluble palladium and gold compoundson the support. The palladium and gold were then reduced by the additionof 1.0 g of 85% hydrazine hydrate to the above mixture. The mixture wasagitated for a few seconds and allowed to stand covered and undisturbedat room temperature for another 23 hours. The supernatant liquid wasdecanted from the catalyst and the catalyst was rinsed four times withwater to remove the small amount of metal sludge present. The catalystwas washed thoroughly by the Column Washing Procedure described below toremove chlorides and residual reagents. The catalyst was dried on astainless steel screen at 60° C. in a forced air oven for 20 to 24hours. The catalyst was analyzed for potassium using AA Analysis. Thenthe catalyst was impregnated with the desired amount of potassiumacetate in water using the impregnation technique described above forthe palladium and gold salts. Then the impregnated catalyst was dried at60° C. for 20 to 24 hours. The palladium, gold, sodium, and potassiumcontents in the finished catalysts were determined by ICP analyses andthe sodium and potassium contents were also determined by AA Analysesfor greater accuracy. The catalysts so produced were shell-impregnated(i.e., substantially all of the palladium and gold was present in ashell within 0.5 mm of the surface of the beads of Support I).

Column Washing Procedure

Catalysts were washed or rewashed in a 1.24 inch o.d.×24 inches glasschromatography column fitted with a Teflon® stopcock. Typically 15 g ofcatalyst was added to the column which was then filled with water. Thestopcock was adjusted to allow the liquid to flow from the column suchthat about one liter passed through the catalyst at room temperatureover a period of about 24 hours. After this period, the excess liquidwas drained from the column and the catalyst removed and dried asdescribed above in the Catalyst Preparation Procedure.

Catalyst Test Method

The catalyst (2.5 g samples of 5 to 6 mm catalyst spheres) was dilutedwith 10.5 ml of 0.5 mm glass beads and the mixture was uniformlydistributed in both legs of a 316-stainless steel U-tube reactor. Thereactor had an outside diameter of 3/8 inch and an overall height ofabout 6 inches. An ethylene flow of 151 ml/min. was started through thereactor after which the catalyst was heated in an oven maintained at150° C. while allowing the system to pressurize to 115 psig. Aftermaintaining at these conditions for 1.5 hours, acetic acid vapor wasadded to the ethylene and the mixture was passed over the catalyst for45 minutes. Air was added to the feed gas at a slowly increasing rateover a 45-minute Period until a total flow of 105 ml./min. was reached.The catalyst was allowed to stabilize for two hours before beginningdata collection. The final gas composition was ethylene:aceticacid:oxygen:nitrogen=52.9:10.7:7.7:28.7, the total gas hourly spacevelocity was about 3800 hr¹, and the acetic acid liquid hourly spacevelocity was about 1 hr⁻¹. The product was analyzed by gaschromatography. The run-to-run reproducibility of the microreactors usedin these experiments is about ±10 STY units.

EXAMPLE I

Support I contains about 0.1 weight percent sodium as received from themanufacturer. An additional 0.4 to 0.8 weight percent of sodium isintroduced during the precipitation step when sodium hydroxide or sodiummetasilicate is used as the precipitating agent. Three catalysts wereprepared using potassium hydroxide as the precipitating agent to reducethe sodium level in the final catalyst. Varying concentrations ofpotassium acetate were added to the precipitating solution to furthershift the ion-exchange equilibrium toward potassium. The catalysts wereprepared from the same master batch having a nominal palladium loadingof 0.58 weight percent and an Au/Pd ratio of 0.46. After reduction withhydrazine and washing using the Column Washing Procedure, the catalystswere analyzed for sodium and potassium. Then additional potassiumacetate was added as required to give a final potassium acetate contentof about 5.3 weight percent. The results given in Table A show that thesodium content of the catalysts was reduced. The sodium content in thecatalysts dropped uniformly and catalytic activity improved as thepotassium concentration of the Precipitating solution was increased.

                  TABLE A                                                         ______________________________________                                        Low Sodium Catalyst Preparations                                              % KOAc (a) % Na (b)     STY    % Selectivity                                  ______________________________________                                        0          0.186        576    93.4                                           2.5        0.121        603    93.2                                           5.0        0.091        597    93.4                                           ______________________________________                                         (a) Wt % potassium acetate added to the precipitating solution.               (b) Wt % sodium calculated to be in the finished catalyst. Based on AA        Analyses prior to KOAc impregnation and the quantity of KOAc added.      

A similar catalyst, prepared using sodium metasilicate as theprecipitating agent (in lieu of potassium hydroxide) had an STY of 544,a selectivity of 93.6 and a sodium content of 0.44 weight percent. Nopotassium acetate was added in the precipitation step.

EXAMPLE II

The effect of sodium on the performance of vinyl acetate catalysts wasstudied using statistically designed experiments and models wereobtained which are useful in predicting the performance of the vinylacetate catalysts produced by the process of this invention as well asvinyl acetate catalysts produced by the processes of the twoabove-mentioned U.S. patent applications filed concurrently herewith.The models predict catalyst activity and selectivity as a function ofsodium content, palladium loading, gold to palladium weight ratio,potassium content and catalyst weight. These models and the data fromwhich they were generated are shown in Tables B and C respectively.

Because the degree of conversion has a major effect on both catalystproductivity and selectivity, meaningful comparisons of catalystvariables can only be done at constant conversion. In order to predictthe effects of catalyst composition at constant conversion, the OxygenConversion Model in Table B was rearranged to express catalyst weight asa function of the palladium content, gold/palladium ratio, potassiumcontent, sodium content and conversion. This catalyst weight term wasthen used to replace the catalyst weight terms in the STY andSelectivity models. The predicted effects of increasing sodium contenton vinyl acetate catalyst activity and selectivity are plotted in FIG.1.

The abbreviations used in Tables B and C have the following meanings:

    ______________________________________                                        The abbreviations used in Tables B and C                                      have the following meanings:                                                  ______________________________________                                        Pd          Weight percent palladium in the catalyst                          Au/Pd       Weight ratio of gold to palladium in                                          the catalyst                                                      Cat.Wt      Catalyst weight in grams                                          K           Weight percent potassium in the catalyst                          Na          Weight percent sodium in the catalyst                             STY         Space time yield in grams of vinyl                                            acetate per liter of catalyst per hour                            R.sup.2     Correlation coefficients which are                                            indicative of the quality of fit of the                                       data to the models                                                RSD         Relative standard derivation                                      EtOAc By-   Production of ethyl acetate in moles/                             Product Rate                                                                              kilogram of catalyst/hour                                         % Heavies   Heavy by-products expressed as a weight                           By-Products percent of the vinyl acetate produced.                            in VA       Heavies by-products are defined as all                                        products which elute after acetic acid                                        in the gas chromatographic analytical                                         procedure.                                                        ______________________________________                                    

Table D shows the effect of varying sodium on catalyst activity aspredicted by the models in Table B.

                                      TABLE B                                     __________________________________________________________________________    MODELS RELATING                                                               PERFORMANCE TO CATALYST COMPOSITION (a)                                       __________________________________________________________________________    Part A                                                                        O.sub.2 Conversion to Vinyl Acetate = 100/(1 + e.sup.Z1)                      Where Z1 =                                                                           0.507 -                                                                            1.907(% Pd-0.743) -                                                                      0.863(Au/Pd-0.584) +                                                                     0.109(% K-2.43) +                                                                       0.459(% Na-0.502)                             (19.6)     (8.1)      (4.5)     (7.0)                                    - .913(Cat.Wt.-1.91) +                                                                    1.438(% Pd-0.743)(Au/Pd-0.584) +                                                               0.551(Au/Pd-0.584)(Cat. Wt.-1.91)                (29.8)      (3.9)            (5.1)                                            + 1.438(% Pd-0.743).sup.2 +                                                               2.779(Au/Pd-0.584).sup.2 +                                                                1.384(% K-2.43).sup.2 +                                                                 0.284(Cat Wt. -1.91).sup.2                  (3.1)       (4.2)       (4.4)     (6.5)          R.sup.2 = 0.988                                                               RSD = 0.103           Part B                                                                        Activity (STY) = e.sup.Z2                                                     Where Z2 =                                                                           6.707 +                                                                            0.942(% Pd-0.743) +                                                                      0.334(Au/Pd-0.584) -                                                                     0.194(% Na-0.502) -                                                                      0.123(Cat.Wt.-1.91)                          (13.6)     (5.6)      (4.0)      (8.1)                                   - 1.438(% Pd-0.743).sup.2 -                                                               0.128(% K-2.43).sup.2                                             (4.3)       (5.6)                                R.sup.2 = 0.922                                                               RSD = 0.079           Part C                                                                        Selectivity to Vinyl Acetate = 100 - e.sup.Z3                                 Where Z3 =                                                                           1.9 +                                                                              0.457(% Pd-0.743) -                                                                      0.118(% K-2.43) -                                                                       0.095(% Na-0.502) +                                                                      0.121(Cat.Wt.-1.91)                           (17.4)     (12.7)    (3.5)      (14.8)                                   + 0.186(% Pd-0.743)(Cat.Wt.-1.91) -                                                             0.254(Au/Pd-0.584)(% K-2.43) -                                                                0.0525(% K-2.43)(Cat.Wt.-1.91)              (5.9)             (6.3)           (4.6)                                       - 0.164(% Na-0.502)(Cat.Wt.-1.91) +                                                              0.038(% K-2.43).sup.2                                      (4.1)              (3.2)                         R.sup.2 = 0.956                                                               RSD = 0.034           Part D                                                                        EtOAc By-Product Rate = e.sup.Z4                                              Where Z4 =                                                                           -3.640 +                                                                           0.9715(% Pd-0.743) -                                                                     1.135(Au/Pd-0.584) -                                                                     0.2189(Cat.Wt.-1.91) -                                                                    0.3743(% Na-0.502)                          (7.5)      (10.7)     (8.1)       (6.4)                                  - 0.267(% K-2.43).sup.2 -                                                                2.428(% Pd-0.743).sup.2                                            (7.2)      (4.1)                                 R.sup.2 = 0.872                                                               RSD = 0.142           Part E                                                                        % Heavies By-Product in VA = e.sup.Z5 (b)                                     Where Z5 =                                                                           0.280 +                                                                            0.441(Au/Pd-0.584) -                                                                     0.254(% K-2.43) -                                                                       0.0694(Cat.Wt.-1.91)                                     (5.2)      (10.5)    (3.1)                  R.sup.2 = 0.797                                                               RSD                   __________________________________________________________________________                                                            = 0.119                (a) Values in parentheses beneath the regression equations are the            observed Tratios.                                                             (b) Based on the amount of vinyl acetate produced.                       

                                      TABLE C                                     __________________________________________________________________________    No.                                                                              % Pd                                                                              Au/Pd                                                                             % K                                                                              % Na                                                                              Cat Wt.                                                                            % O.sub.2 Conv                                                                      STY % Selectivity                                __________________________________________________________________________    DESIGN DATA (a)                                                                1 0.80                                                                              0.70                                                                              2.23                                                                             0.51                                                                              1.64 34.4  897.6                                                                             93.2                                          2 0.80                                                                              0.70                                                                              2.23                                                                             0.51                                                                              1.65 37.1  941.5                                                                             92.9                                          3 0.80                                                                              0.70                                                                              2.23                                                                             0.51                                                                              1.65 34.8  923.3                                                                             93.2                                          4 1.05                                                                              0.91                                                                              3.67                                                                             0.26                                                                              0.73 16.1  1181.7                                                                            94.4                                          5 0.57                                                                              0.46                                                                              2.33                                                                             0.14                                                                              0.73  7.1  759.2                                                                             94.6                                          6 0.54                                                                              0.89                                                                              2.27                                                                             0.16                                                                              2.50 44.9  727.4                                                                             92.5                                          7 1.13                                                                              0.96                                                                              2.35                                                                             0.18                                                                              0.75 21.0  1262.4                                                                            94.1                                          8 0.52                                                                              0.44                                                                              3.51                                                                             0.17                                                                              0.76  5.8  553.2                                                                             94.5                                          9 1.14                                                                              0.46                                                                              2.35                                                                             0.19                                                                              2.50 66.1  912.3                                                                             89.7                                         10 0.53                                                                              0.91                                                                              3.64                                                                             0.14                                                                              2.51 32.7  595.0                                                                             94.4                                         11 1.05                                                                              0.47                                                                              3.68                                                                             0.18                                                                              2.50 55.7  847.4                                                                             92.1                                         12 1.08                                                                              0.87                                                                              2.80                                                                             0.73                                                                              0.76 17.5  1158.0                                                                            93.8                                         13 0.52                                                                              0.46                                                                              1.50                                                                             0.37                                                                              0.72  6.6  569.0                                                                             94.0                                         14 0.52                                                                              0.85                                                                              1.40                                                                             0.50                                                                              2.50 38.4  587.4                                                                             91.5                                         15 1.08                                                                              0.94                                                                              1.40                                                                             0.54                                                                              0.74 19.3  1111.7                                                                            92.1                                         16 0.55                                                                              0.42                                                                              2.70                                                                             0.44                                                                              0.76  5.9  617.2                                                                             94.3                                         17 1.10                                                                              0.45                                                                              1.40                                                                             0.59                                                                              2.54 57.7  769.9                                                                             89.7                                         18 0.55                                                                              0.91                                                                              2.90                                                                             0.40                                                                              2.54 34.7  629.5                                                                             94.1                                         19 1.09                                                                              0.47                                                                              2.80                                                                             0.50                                                                              2.52 56.6  865.0                                                                             91.5                                         20 0.82                                                                              0.70                                                                              2.12                                                                             0.49                                                                              1.63 35.2  901.9                                                                             93.0                                         21 0.82                                                                              0.70                                                                              2.12                                                                             0.49                                                                              1.62 35.7  925.7                                                                             92.9                                         22 0.78                                                                              0.65                                                                              2.12                                                                             0.53                                                                              2.52 50.6  793.2                                                                             92.2                                         23 0.78                                                                              0.65                                                                              2.12                                                                             0.53                                                                              1.63 33.3  884.2                                                                             93.4                                         24 1.07                                                                              0.83                                                                              2.93                                                                             0.69                                                                              2.53 51.8  822.1                                                                             92.5                                         25 0.53                                                                              0.36                                                                              2.96                                                                             0.44                                                                              2.52 28.5  506.7                                                                             93.4                                         26 1.07                                                                              0.82                                                                              1.47                                                                             0.56                                                                              2.50 54.3  709.7                                                                             88.7                                         27 1.07                                                                              0.82                                                                              1.47                                                                             0.56                                                                              2.51 52.4  701.7                                                                             89.3                                         28 0.56                                                                              0.82                                                                              3.02                                                                             0.42                                                                              0.75  7.7  733.8                                                                             95.0                                         29 1.02                                                                              0.46                                                                              2.88                                                                             0.48                                                                              0.75 14.1  966.6                                                                             93.8                                         30 0.54                                                                              0.44                                                                              1.51                                                                             0.36                                                                              2.50 29.6  483.5                                                                             92.7                                         31 0.54                                                                              0.80                                                                              1.48                                                                             0.50                                                                              0.75 10.8  763.7                                                                             94.0                                         32 1.08                                                                              0.43                                                                              1.47                                                                             0.63                                                                              0.75 13.1  889.6                                                                             93.2                                         33 0.80                                                                              0.66                                                                              2.12                                                                             0.92                                                                              1.64 33.0  871.5                                                                             93.2                                         34 0.80                                                                              0.66                                                                              2.12                                                                             0.92                                                                              1.62 32.3  866.6                                                                             93.5                                         35 1.13                                                                              0.62                                                                              2.10                                                                             0.59                                                                              1.62 43.1  1066.2                                                                            92.4                                         36 0.41                                                                              0.61                                                                              2.20                                                                             0.37                                                                              1.64 21.3  621.8                                                                             94.2                                         37 0.76                                                                              0.87                                                                              2.10                                                                             0.55                                                                              1.62 33.3  881.8                                                                             93.7                                         38 0.76                                                                              0.34                                                                              2.10                                                                             0.45                                                                              1.65 27.5  734.0                                                                             93.4                                         39 0.77                                                                              0.61                                                                              2.10                                                                             0.52                                                                              0.43  9.9  1246.7                                                                            93.7                                         40 0.77                                                                              0.61                                                                              2.10                                                                             0.52                                                                              2.86 56.9  745.8                                                                             91.7                                         Supplemental Data (b)                                                         41 0.56                                                                              0.39                                                                              2.19                                                                             0.44                                                                              2.54 36.0  607.8                                                                             93.5                                         42 0.57                                                                              0.39                                                                              2.19                                                                             0.15                                                                              2.54 38.4  612.0                                                                             92.7                                         43 0.54                                                                              0.39                                                                              3.38                                                                             0.68                                                                              2.54 25.8  482.8                                                                             94.1                                         44 0.55                                                                              0.39                                                                              3.38                                                                             0.28                                                                              2.54 30.9  545.9                                                                             93.5                                         45 0.56                                                                              0.39                                                                              2.79                                                                             0.28                                                                              2.54 36.4  605.5                                                                             93.4                                         46 0.56                                                                              0.39                                                                              2.79                                                                             0.16                                                                              2.54 37.2  610.9                                                                             92.9                                         47 0.54                                                                              0.39                                                                              2.79                                                                             0.96                                                                              2.54 27.4  493.2                                                                             93.8                                         48 0.54                                                                              0.39                                                                              3.62                                                                             0.36                                                                              2.54 27.2  492.4                                                                             93.7                                         49 0.57                                                                              0.39                                                                              1.95                                                                             0.20                                                                              2.54 35.3  571.0                                                                             92.9                                         50 0.54                                                                              0.39                                                                              3.70                                                                             0.39                                                                              2.54 27.1  483.8                                                                             93.9                                         51 0.55                                                                              0.39                                                                              2.12                                                                             1.25                                                                              2.54 27.4  494.1                                                                             94.1                                         52 0.50                                                                              0.39                                                                              3.95                                                                             2.39                                                                              2.54 13.4  283.9                                                                             94.3                                         53 0.56                                                                              0.39                                                                              2.25                                                                             0.50                                                                              2.54 33.6  609.3                                                                             93.5                                         54 0.57                                                                              0.39                                                                              2.25                                                                             0.12                                                                              2.54 34.9  641.5                                                                             93.1                                         55 0.55                                                                              0.39                                                                              2.25                                                                             1.01                                                                              2.54 28.7  540.0                                                                             94.1                                         __________________________________________________________________________     (a) Unless otherwise indicated, the palladium and gold values were            determined by ICP and the sodium and potassium values were determined by      Atomic Absorption Analysis.                                                   (b) The catalysts were prepared by addition of sodium and potassium           acetates to Catalyst II that had been rewashed as described in U.S. Pat.      application 07/793,127, entitled Alkenyl Alkanoate Catalyst Process filed     concurrently herewith. Reported compositions are calculated from the          analysis of this catalyst and the quantities of sodium and potassium          acetate added.                                                           

                  TABLE D                                                         ______________________________________                                        Predicted Effect of Sodium on Catalyst* Activity                              % Na         STY    % Improvement**                                           ______________________________________                                        0.1          665     0.0                                                      0.2          649     2.5                                                      0.3          633     5.1                                                      0.4          618     7.6                                                      0.5          603    10.3                                                      0.6          581    14.5                                                      0.7          574    15.9                                                      0.8          560    18.8                                                      0.9          546    21.8                                                      ______________________________________                                         *For a catalyst composition set at: 0.58% Pd, Au/Pd = 0.45 and 2.2% K and     an oxygen conversion set at 35%.                                              **Predicted percent change in STY resulting from decrease in sodium           content from amount shown in first column to 0.1%.                       

EXAMPLE III

The procedure of Example 1 of U.S. Pat. No. 4,048,096 (Bissot) wasrepeated as follows: Two preparations (Runs 1 and 2) were made, eachemploying 15 g of Support I, 0.315 g of Na₂ PdCl₄, 0.085 g of HAuCl₄,0.585 g of Na₂ SiO₃.9H₂ O, 0.59 g of 85% hydrazine hydrate, and 0.823 gof potassium acetate. Since the exact washing procedure is not disclosedin Example 1 of Bissot the catalyst of Run 1 was washed using the ColumnWashing Procedure for 16 hours using 23 ml of H₂ O per gram of catalystwhereas the catalyst of Run 2 was similarly washed but with 31 ml of H₂O per gram of catalyst. The catalysts of Runs 1 and 2 were analyzed byICP for palladium and gold and by AA Analysis for potassium and sodium.The experimental error of the sodium determination is estimated to beabout ± 0.01 relative percent. The catalyst of Run 1 was analyzed induplicate. The results are shown in Table E.

                  TABLE E                                                         ______________________________________                                        % Pd      % Au    % K     % Na  STY    Selectivity                            ______________________________________                                        Run 1 0.544   0.201   2.34  0.32  550    93.9                                 Run 1 0.556   0.204   2.35  0.32                                              Run 2 0.552   0.195   2.34  0.38  535    93.7                                 Bissot                                                                               0.578*  0.242*  2.08*                                                                              --     560**  93**                                ______________________________________                                         *Calculated based on the data in Example 1 of Bissot                          **Disclosed in Example 1 of Bissot                                       

EXAMPLE IV

The measured activities of three commercial catalysts (Catalysts X, Yand Z) are shown in Table F. In Table F, the activities of Catalysts Xand Y are compared to the predicted activities of catalysts of thisinvention having the same composition ("Model Catalysts"). The predictedactivities were determined from the models of Table B and assuming a0.15% level of sodium. The Model Catalysts had markedly higher predictedactivities. A similar comparison could not be made for Catalyst Zbecause its composition is outside the range of the models of Table B.

Catalyst X was prepared using the Catalyst Preparation Procedure. Thepreparation of Catalyst X differed from the preparation of catalyst Y inthat, in the preparation of Catalyst Y: (1) the catalyst was driedbefore precipitation and (2) the precipitating agent used was sodiumhydroxide rather than sodium metasilicate. The reduction, washing,drying and potassium acetate impregnation steps were the same for bothcatalyst preparations.

With reference to Catalyst Y, the suffixes A, B and C in Table F denotedifferent preparations ("lots") of nominally the same catalyst and, withrespect to Catalysts Y and Z, the suffixes 1 and 2 denote duplicateanalyses of different samples from the same lot of the catalysts.

Catalyst Z has a high palladium content and uses a cadmium co-catalystrather than gold. Cadmium is significantly more toxic than gold. Inaddition, Catalyst Z is prepared by a process substantially differentfrom the process of this invention, that is, Catalyst Z is prepared byimpregnating a support with a solution of palladium, cadmium andpotassium acetates and drying. There are no precipitation, reduction orwashing steps in the process used to produce Catalyst Z.

                  TABLE F                                                         ______________________________________                                                 % Pd  % Au    % Cd    % K  % Na  STY                                 ______________________________________                                        Catalyst X*                                                                              0.53    0.22    0     2.36 0.54  272                               Model Catalyst                                                                           0.53    0.22    0     2.36 0.15  589                               Catalyst YA-1*                                                                           0.49    0.19    0     2.29 0.60  360                               Model Catalyst                                                                           0.49    0.19    0     2.29 0.15  546                               Catalyst YA-2*                                                                           0.49    0.19    0     2.31 0.60  360                               Model Catalyst                                                                           0.49    0.19    0     2.31 0.15  545                               Catalyst YB*                                                                             0.63    0.24    0     2.27 0.70  386                               Model Catalyst                                                                           0.63    0.24    0     2.27 0.15  669                               Catalyst YC-1*                                                                           0.61    0.24    0     2.24 0.69  395                               Model Catalyst                                                                           0.61    0.24    0     2.24 0.15  653                               Catalyst YC-2*                                                                           0.61    0.26    0     2.18 0.70  395                               Model Catalyst                                                                           0.61    0.26    0     2.18 0.15  658                               Catalyst Z-1*                                                                            2.16    0         1.88                                                                              1.89 0.08  685                               Model Catalyst                                                                           Outside range of models                                            Catalyst Z-2*                                                                            2.16    0         1.89                                                                              1.92 0.09  685                               Model Catalyst                                                                           Outside range of models                                            ______________________________________                                         *Comparative Catalysts                                                   

What is claimed is:
 1. A process for producing a catalyst that is usefulin catalyzing the reaction of an alkene, an alkanoic acid and anoxygen-containing gas to produce an alkenyl alkanoate and that comprisessupport particles which are capable of exchanging cations and which areimpregnated with palladium, gold and potassium acetate, said processcomprising the steps of:(a) impregnating the support particles withaqueous solutions of water-soluble palladium and gold compounds; (b)precipitating water-insoluble palladium and gold compounds onto thesupport particles from such solutions using a precipitating agent; (c)converting the precipitated water-insoluble palladium and gold compoundsto palladium and gold on the support particles using a reducing agent;(d) washing the support particles with water; (e) drying the supportparticles; (f) further impregnating the support particles with apotassium promoter selected from the group consisting of potassiumalkanoates and any potassium compound that is converted to a potassiumalkanoate during said reaction; and (g) drying the impregnated particlesto produce the catalyst; and said process being conducted by employingessentially sodium-free starting materials in steps (b) and (c) so as toreduce the amount of sodium in the catalyst and thereby to increase theactivity of the catalyst.
 2. A process as claimed in claim 1 whereinpotassium hydroxide is used as the precipitating agent in step (b).
 3. Aprocess as claimed in claim 2 wherein potassium salt is used to aid inthe displacement of sodium bound on the carrier by the potassiumprecipitating agent.
 4. A process as claimed in claim 1 wherein thecatalyst produced by the process has no more than 0.3 weight percentsodium based on the weight of the catalyst.
 5. A process as claimed inclaim 1 wherein the catalyst produced by the process has no more than0.2 weight percent sodium based on the weight of the catalyst.
 6. Aprocess as claimed in claim 1 wherein the catalyst produced by theprocess has no more than 0.1 weight percent sodium based on the weightof the catalyst.